One of the most common mechanical fastening systems in use today is a bolt or screw having a threaded shaft and a head on one end wherein a nut is threaded onto the shaft at an opposite end. The threaded shaft is typically received in a hole in the work piece or multiple work pieces and captured between the head and the nut. The items are then secured by rotating the nut on the threaded shaft until the work piece is secured between the nut and the head. As this simple fastening system became more widely adopted in industry, users discovered that over time, regardless of the degree of torque applied to tighten the nut, the nut would eventually loosen. This undesirable characteristic was discovered to be even more pronounced in applications where the assembly was subject to vibration, widely varying thermal cycles, and mechanical shock. Still other uses of threaded shafts and nuts include applications where a nut is desired to be secured at a desired position along the threaded shaft without necessarily being torqued against a work piece.
In an attempt to maintain the desired position of the nut or to maintain a desired torque on the bolt and nut combination, various means of locking the nut to the threaded shaft have been implemented. Some of these means include a resilient lock washer, a small set-screw threaded into the side of the nut engaging the threads of the bolt shaft, a resin ring molded interiorly to the nut threads and closely engaging the threads of the shaft, and even utilizing a safety wire through a hole in the nut and fastened to a separate structure. The above methods of preventing the loosening or repositioning of nuts have enjoyed various degrees of success. Some have been incorporated with relative ease of installation, but have not been very successful in maintaining the desired torque. Others have been incorporated with reasonable success in maintaining the desired torque, but have been difficult to install.
In those applications wherein the nut is desired to be positionally retained on the threaded shaft and not able to be torqued against a work piece, the most common means of securing the nut in place is to thread a second, or blocking, nut on the shaft and abutting the first nut thereby blocking the unwanted rotation of the first nut. Opposing torque is then applied to the abutting nuts and the dual nut combination is positionally fixed along the shaft by the friction between the abutted faces of the nuts and the opposing frictional force of the nut threads against the threads of the shaft. However, a pair of opposingly torqued nuts is subject to the same thermal, vibrational, and shock environments discussed above that lead to eventual unwanted disengagement of the nuts.
Thus what is desired is an ensemble of blocking nuts that is simple to install and in addition will reliably maintain its desired position throughout the life of the mechanism on which it is installed.